S2k guideline for diving accidents

For the purposes of this guideline, a diving accident is defined as an event that is either potentially life-threatening or hazardous to health as a result of a reduction in ambient pressure while diving or in other hyperbaric atmospheres with and without diving equipment. This national consensus-based guideline (development grade S2k) presents the current state of knowledge and recommendations on the diagnosis and treatment of diving accident victims. The treatment of a breath-hold diver as well as children and adolescents does not differ in principle. In this regard only unusual tiredness and itching without visible skin changes are mild symptoms. The key action statements: on-site 100% oxygen first aid treatment, immobilization/no unnecessary movement, fluid administration and telephone consultation with a diving medicine specialist are recommended. Hyperbaric oxygen therapy (HBOT) remains unchanged as the established treatment in severe cases, as there are no therapeutic alternatives. The basic treatment scheme recommended for diving accidents is hyperbaric oxygenation at 280 kPa.


Objective
This guideline represents the current state of knowledge and recommendations on the diagnosis and treatment of diving accident victims with regard to: • First aid by lay persons as well as treatment by medical assistants and physicians • The sequence of rescue chain deployment and the transportation of diving accident victims • Initial hyperbaric medical treatment of diving accident victims • The further medical care of diving accident victims

Basic methodological principles
The methodological approach adopted in the development of the guideline is set out in the Guideline Report. This is freely available online, e.g., on the AWMF website (http:// www.awmf.org/).

.1 Definition
What is the definition of a "diving accident"?
For the purposes of this guideline, a "diving accident" is defined as an event that is either potentially life-threatening or hazardous to health as a result of a reduction in ambient pressure while diving or in other hyperbaric atmospheres with and without diving equipment.
-Yes: 11/11, no: 0, abstentions: 0 -Strength of consensus: 100% (strong consensus) The suspected diagnosis of "diving accident" is likely in the presence of the following conditions [1]: • breathing was performed using diving equipment under water, irrespective of the breathing gas/breathing gas mixture used (potentially only a single breath), or • breathing was performed using air that had collected under water (e.g., in a wreck or cave), or • breath-hold dives were performed (generally several deep dives) [2], [3] and • mild and/or severe symptoms are present (see section 3).
Can the "diving accident" guideline be used for breathhold diving?
If, following a dive, a breath-hold diver develops symptoms of a diving accident consistent with the definition applied herein, this guideline shall be used.
-Yes: 11/11, no: 0, abstentions: 0 -Strength of consensus: 100% (strong consensus) There is no clear definition for the term "diving accident," either nationally or internationally. Both in daily routine and in the literature this term is sometimes used to refer to all medical incidents and events occurring in temporal relation to diving. However, diving incidents need not necessarily be associated with hyperbaric exposure, e.g., myocardial infarction while diving. Likewise in the case of incidents associated with hyperbaric exposure, there is a broad range of relevant disorders, such as barotrauma and submersion pulmonary edema, over and above the diving accidents defined in this guideline. As a general principle, one should assume that a diving accident has occurred in the event of a medical incident in temporal relation to diving. A diving accident, according to the definition in this guideline, is characterized by the formation or introduction of gas bubbles in(to) blood and tissues. These processes can lead to decompression sickness. Other terms used in English include "decompression incident" or "decompression injury," for which the internationally accepted abbreviation is "DCI." In German, the term "decompression accident" (Dekompressionsunfall) is also used. Irrespective of the mode in which they develop, diving accidents can be subdivided into: • Decompression sickness (DCS) and • Arterial gas embolism (AGE) (see Figure 1: Classification of diving accidents)

Etiology and pathophysiology 2.2.1 Decompression sickness
Bubble formation is assumed to be the primary mechanism of injury in decompression sickness. Divers absorb inert gas (nitrogen when breathing air) into their tissues when they inhale compressed gas during a dive. During ascent the partial pressure of the dissolved gas in tissue can exceed the ambient pressure (oversaturation), resulting in the formation of bubbles in these tissues or in the blood flowing through them. The resulting venous bubbles, although small (19-700 µm) [4], are very common following dives [5] or rapid exposure to altitude [6]. They are normally filtered through pulmonary capillaries and are asymptomatic. However, venous gas bubbles can reach the arterial circulation by overwhelming the filtering capacity of the pulmonary capillary network or by crossing over through intrapulmo-nary or intracardiac right-to-left shunts, such as atrial septal defects or patent foramen ovale (PFO). The presence of a PFO increases the likelihood of decompression sickness in the brain, spinal cord, inner ear, and skin [7], [8] , [9], presumably since tiny arterialized venous gas bubbles that enter the capillaries of oversaturated tissue following a dive grow through inert gas diffusion (nitrogen) [10]. The formation of bubbles in tissue can cause mechanical dysfunction and focal hemorrhage, particularly in the white matter of the spinal cord [11]. Even small intravascular bubbles can have physical sequelae involving inflammatory and thrombogenic responses. Intravascular bubbles can result in impaired regulation of vascular tone, plasma leaks, and hypovolemia [12]. As a result of this mechanism, a large number of venous gas bubbles can injure the pulmonary capillaries and lead to pulmonary edema [13].

Arterial gas embolism
AGE can occur in divers when compressed gas becomes trapped in the lungs and the ambient pressure drops during ascent to the surface. Expansion of the gas results in rupture of the alveolar capillary membrane as well as the entry of gas into the pulmonary vascular system. This can be caused by inadequate expiration of expanding gas from the entire lung or local disease such as bronchial obstruction or bullae. Even slight differences in pressure on ascent from a depth of only 1 m can be causal here [14]. Large intraarterial bubbles can cause arterial occlusion, ischemia, and infarction. Secondary effects in the brain following bubble-induced ischemia are likely to be similar to processes that occur after a stroke, including the release of excitatory neurotransmitters, oxidative stress, inflammation, and an immune response [15].

Prevention
Despite adhering to all safety standards when diving, it is not possible to completely rule out the occurrence of a diving accident. Prevention involves the diver assuming a high degree of personal responsibility. In order to meet this requirement and to be able to make appropriate decisions, the diver must be aware of the relevant influencing factors and their effects, as well as the options to correct these where necessary. All dives should be preceded by dive training and dive planning that is appropriate to the dive. Regular skills training (including self and third-party rescue) and general physical fitness form an important basis for safe diving. Fundamental to any assessment is a medical history, which depends to a crucial extent on truthful information from the diver, as well as a qualified diving medical examination ("diving fitness"); this consists of a clinical examination and instrument-based examinations (e.g., ECG, stress ECG where appropriate, lung function, otoscopy). In addition to the detection of absolute contraindications (e.g., seizure disorders, impaired cardiovascular performance), a proactive consultation is also a key component of any diving medical examination. This consultation always includes general aspects for all divers as well as individual aspects arising from possible risk factors or examination findings. The general consultation is complementary to the contents of the diver training and should include, for example, the aspect of dehydration risk (lack of fluid intake, fluid loss through sweating and/or diarrhea, etc.) or information on temperature balance and behavior in the case of transient sicknesses. Depending on the diver being examined, the individual part of the consultation is multilayered and can include subjects such as behavior in the case of overweight (e.g., ensuring adequate physical fitness and following the "low bubble diving" rule), sea sickness, chronic diseases, and medication, not least depending on the planned dive. In the case of relative contraindications, a discussion should be had with the diver regarding how this increased risk for a diving accident can be reduced by appropriate measures. The dive itself can be made safer through good and conservative dive planning, e.g., according to the low-bubble diving rule. Prior to each dive, the diver also needs to assess his or her own health status to determine whether factors that hinder safety are present. Behavior following a dive can also affect the risk for the occurrence of a diving accident. For example, increased physical exertion (difficult exit from the water or carrying heavy pieces of equipment) or short intervals before subsequent flights increase the risk of bubbles being released and circulated.

Symptoms and diagnosis
Which examination methods are suitable for the diagnosis, differential diagnosis, and follow-up of a decompression accident?
All new-onset symptoms after a dive shall be considered as a possible diving accident unless some other mechanism of onset is apparent. The broad diversity in the clinical picture of DCI hampers diagnosis. The diagnosis of DCI and any differential diagnoses that may need to be taken into account need to be assessed on the basis of clinical symptoms. Complementary technical investigations are not required for the diagnosis of DCI. However, these may be needed in order to distinguish between differential diagnoses. Due to the frequency of neurological symptoms [16], [17], all divers in whom a diving accident is suspected should undergo a neurological examination. A lay examination by first responders according to a predefined examination procedure (see Attachment 1) can enable early recogni-tion of neurological symptoms as well as follow-up documentation of symptom severity. On completion of a dive, symptoms of a diving accident can rapidly change before and after the initiation of treatment; therefore, follow-up examinations are required.
Which classification is suitable for the assessment of severity of a diving accident?
The treatment approach differs depending on whether symptoms are mild or severe. Therefore, this guideline classifies diving accident severity according to this classification (see section 3.1 and 3.2).
-Yes: 10/10, no: 0, abstentions: 0 -Strength of consensus: 100% (strong consensus) The international literature describes a number of classifications of diving accidents. The best known of these remains the traditional classification that is still used worldwide today, which subdivides decompression accidents into DCS I: bends, pain only, mild, minor symptoms, DCS II: severe, serious, major symptoms, and arterial gas embolism (AGE). Modified classifications that also distinguish between "mild symptoms" and "serious symptoms" have been advocated. The classification into mild symptoms and severe symptoms used in this guideline differs from the majority of classifications in international use in order to adequately treat patients with apparently "milder" symptoms both consistently and at an early stage, thereby avoiding late sequelae or complications. This guideline classifies diving accident severity according to the following classification.

First-aid measures
Which measures are first-aiders recommended to take?
Measures for mild symptoms (see Figure 2) • Immediate breathing of 100% oxygen or breathing gas with the highest available oxygen content irrespective of the gas mix used during diving [19], [20] (see section 4.4) • Checking consciousness, ability to move, and perception (e.g., "Basic neurological assessment for divers," see Attachment 1) • Divers that are able to drink unaided should be encouraged to drink 0.5-1 l fluids/h [18], [21], [22] (preferably isotonic, non-carbonated beverages/no alcoholic beverages) • Protect against both cooling down and overwarming [23], [24]  Measures for severe symptoms (see Figure 2) In the case of unconscious divers without identifiable independent breathing, the recommendations on resuscitation measures according to the current international guidelines apply 2 .

Oxygen therapy/oxygen administration (normobaric oxygenation)
Which method of oxygen administration should be preferred?
For the administration of oxygen, the method that delivers the highest proportion of oxygen available for breathing or ventilation of the victim should be selected. The conservation of resources plays a secondary role here.

Treatment during transportation
Clinical and orienting neurological examination to be regularly repeated.

Hyperbaric oxygen therapy
When is HBOT indicated following a diving accident?

The indication for HBOT is met in the case of:
• Mild symptoms that do not resolve even after 30 min breathing 100% pure oxygen • Severe symptoms (HBOT always indicated) -Yes: 7, no: 0, abstentions: 0 -Strength of consensus: 100% (strong consensus) -This vote was held with and without members of the guideline group with conflicts of interest regarding the recommendations on HBOT. Strong consensus emerged for the recommendations listed here with and without abstentions (10 of 10).

Measures prior to initial HBOT treatment
Imaging is not routinely required. If pneumothorax is suspected, imaging shall be performed.
• Chest X-ray • Ultrasound or • Computed tomography If a further diagnostic work-up according to emergency medicine standards is urgently indicated to rule out other causes of the victim's condition, the delay to HBOT should be as short as possible.
The following measures may be required: • Pleural drainage • Paracentesis in unconscious patients if this can be performed by an expert without a time delay • Urinary catheter

Treatment tables
Which treatment tables should be used?
-Yes: 7, no: 0, abstentions: 0 -Strength of consensus: 100% (strong consensus) -This vote was held with and without members of the guideline group with conflicts of interest regarding the recommendations on HBOT. Strong consensus emerged for the recommendations listed here with and without abstentions (10 of 10).
Does the treatment method depend on the breathing gas used?
The standard 'US Navy Treatment Table 6' shall be used for all diving accidents, irrespective of the breathing gas used by the diving accident victim.
-Yes: 10, no: 0, abstentions: 0 -Strength of consensus: 100% (strong consensus) HBOT can be shortened in the case of complete resolution of the symptoms listed below within the first 10 min of hyperbaric oxygenation at 280 kPa.
• Constitutional or nonspecific symptoms: marked tiredness • Cutaneous symptoms: skin changes, skin bends • Lymphatic symptoms: local swelling • Musculoskeletal symptoms: joint and limb pain • Mild subjective peripheral neurological sensory disturbances without identifiable pathological findings In such cases, treatment can be shortened in line with 'US Navy Treatment Table 5' or similar tables. However, it is essential that no additional symptoms are (or have been) present. If complaints or symptoms fail to (completely) resolve under hyperbaric oxygenation, the initial HBOT treatment is prolonged. At a treatment pressure of 280 kPa, a maximum of two 25-min extensions (20 min oxygen breathing and 5 min air breathing) are performed; at a treatment pressure of 190 kPa, a maximum of two 75-min extensions (3x 20 min oxygen breathing and 3x 5 min air breathing) are also performed.
• If the treated diver is not almost symptom-free after 60 min (3x 20 min) of oxygen breathing at the initial treatment pressure of 280 kPa, an initial extension of 20 min oxygen breathing and 5 min air breathing is performed at this treatment pressure. • If the treated diver is not almost symptom-free after 80 min (4x 20 min) oxygen breathing at 280 kPa, a second extension of 20 min oxygen breathing and 5 min air breathing is performed. Decompression is then performed to 190 kPa according to 'US Navy Treatment Table 6'.  Table 6" • If the treated diver is not almost symptom-free after 60 min (3x 20 min) oxygen breathing at a treatment pressure of 190 kPa, a third extension of a further 60 min (3x 20 min) oxygen breathing and 15 min (3x 5 min) air breathing is then performed after a total of 120 min (6x 20 min) oxygen breathing at this pressure. • If the treated diver is not almost symptom-free after 60 min (3x 20 min) oxygen breathing at a treatment pressure of 190 kPa, a third extension of a further 60 min (3x 20 min) oxygen breathing and 15 min (3x 5 min) air breathing is then performed after a total of 120 min (6x 20 min) oxygen breathing at this pressure. After a total of 240 min oxygen breathing at 190 kPa, decompression to ambient pressure is then performed according to 'US Navy Treatment Table 6'.
Other treatment tables, in particular tables with longer treatment times and higher treatment pressures, as well as mixed gas and saturation treatment tables, should be reserved for centers and personnel with special experience, knowledge, and suitable equipment that allow them to deal with adverse events and outcomes. Oxygen-enriched breathing gas mixtures are to be used for all treatment tables. If HBOT is indicated in the case of inadequate decompression without symptoms, shorter treatment tables are possible, for example, 'US Navy Treatment Table 5' or the 'Problem Wound Treatment Protocol' (see Figure 4). If initial HBOT fails to achieve an improvement, the differential diagnosis needs to be reviewed. • There is no evidence for a benefit from physiotherapy during HBOT versus physiotherapy alone between HBOT treatments. • Pharmacological and further treatment is carried out according to the clinical picture and in accordance with the specialties involved.

Further HBOT treatments
Are follow-up HBOT treatments recommended?
If symptoms are still present following the initial HBOT treatment, a follow-up session should take place within 24 h. • At least 1x daily HBOT, e.g., according to the Problem Wound Treatment Protocol [33]. • If severe neurological symptoms persist, a second HBOT treatment can also be considered according to the standard 'US Navy Treatment Table 6'. • Other treatment tables should be reserved for centers and personnel with special experience, knowledge, and suitable equipment that allow them to deal with adverse events and outcomes.

Decision-making on discontinuation of HBOT
• HBOT can be discontinued following complete and lasting freedom from symptoms. • If, after several treatments, there is no further improvement in symptoms over 3-5 days after an initial improvement under continued treatment, HBOT should be discontinued.

Treatment of children and adolescents
What is the treatment for children and adolescents?

Transfer (secondary transport)
If symptoms persist following initial HBOT, further treatments may need to be carried out within 24 h if the diagnosis is confirmed. If on-site inpatient medical care is not available between HBOT treatments, the patient must be transported to an appropriately equipped treatment center 3 . The means of transport is chosen taking into account the patient's status, the distance and time to the center, and the possible "means of transport." • Helicopter • Air ambulance • Passenger aircraft • Boat • Land-based rescue vehicles There is no reliable data to support a blanket requirement for transport under 1-bar conditions for secondary transportation. Aircraft with normal cabin pressure (e.g., 0.8 bar absolute) are much faster and easier to organize. There is evidence that DCI recurrences following HBOT are more common during or after a flight than in patients that do not fly. There is also evidence that the onset of symptoms of higher severity is not expected during a flight and that treatment prospects are not worsened. Transport by air at normal cabin pressure (e.g., 0.8 bar absolute) does not represent a fundamental obstacle to the transportation of patients following HBOT. The decision to use this means of transport should be made based on: a) the previous course of decompression sickness and b) the severity of ongoing symptoms. There are no uniform international recommendations specifying the time interval after which, and after how many HBOT treatments, DCI patients should be transported by air and at what cabin pressure. These decisions should be made on a case-by-case basis in consultation with experienced diving physicians.

Medical care during secondary transport
The need for and extent of medical care during transportation depends on the severity of the clinical picture.
• Procedures according to emergency medicine/intensive care standards • Oxygen breathing must be possible • Fluid balancing • Clinical and neurological monitoring • Documentation, e.g., emergency physician/intensive care transport protocol • Patients with no or minimal residual symptoms following primary treatment can be transported on a normal scheduled flight.

Rehabilitation
Which rehabilitation measures are recommended following a decompression incident?
Following a diving accident, the specialty and form (outpatient, inpatient) of a rehabilitation measure should be determined on the basis of the specific functional impairment and its extent.
-Yes: 10, no: 0, abstentions: 0 -Strength of consensus: 100% (strong consensus) • Diving accidents can lead to neurological, psychological, cardio-circulatory, pulmonary, constitutional, and orthopedic impairments [64], [17]. Neurological symptoms are often the cause of lasting physical impairments. • Extent and type, or extent of functional impairment, are central to the choice of rehabilitation measure. • There are neither specific rehabilitation programs for diving accident patients nor studies on rehabilitation programs for diving accident victims. • Type, duration, and intensity of rehabilitation measures following a diving accident are based on comparable disorders of other etiology.

Fitness to dive following a diving accident
How should fitness to dive be assessed following a diving accident?
The assessment of fitness to dive following a diving accident shall be made in accordance with the recommendations of the national and international specialist societies for diving medicine or, where applicable, the relevant national legislation.
-Yes: 10, no: 0, abstentions: 0 -Strength of consensus: 100% (strong consensus) The precondition for a re-assessment of fitness to dive is the definitive completion of diving accident therapy and the stability of the treatment outcome, even in the case of residual effects. Any re-assessment of fitness to dive shall be carried out by an experienced physician 1 with advanced training in diving medicine. They are additionally required to have practical experience in the treatment of diving accidents. For commercial divers, special national legal provisions apply, including the associated occupational medical screening and fitness-to-dive tests.

Quality management
Guidelines are intended to form a good information basis, provide orientation and, as decision-making aids, promote the transfer of the best available evidence from clinical studies and the professional expert consensus into everyday care [65]. Guidelines can also support concrete decision-making and action processes, particularly in rare emergencies. Metrics will be developed and recorded in order to evaluate the application and verify the implementation of this guideline. Taking into consideration the treatment workflow, parameters are to be defined that evaluate process, structure, and, if necessary, outcome quality. In the following, the guideline group has drawn up proposals for indicators and parameters that will be further developed and whose application will become established following the publication of this guideline.
To this end, it would be possible in principle to use routine administrative data, e.g., from the data sets of the DIVI emergency physician protocol and emergency admission register [66], as well as, if necessary, data from a national HBOT registry in Germany that is to be developed.

Pre-hospital performance indicators
Taking into consideration the treatment workflow, parameters have been described and performance indicators formulated (see Table 1).

Post-inpatient performance indicators
If a patient is transferred with residual effects following a diving accident, the transfer report should indicate the need for rehabilitation measures and a further, post-inpatient follow-up examination.
6. Patients with residual effects following a diving accident shall be examined for sequelae for 4-6 weeks. → "outcome"

Update planning
The application and implementation of the guideline shall be evaluated prior to its update.

Guideline report
The methodological approach to the development of the guideline and, in particular, the management of potential conflicts of interest is presented in the guideline report. This is freely available online, e.g., on the website of the Association of the Scientific Medical Societies in Germany (AWMF) [67].

Competing interests
See